JP7718360B2 - Resin current collector and laminated battery - Google Patents

Description

The present disclosure relates to a resin current collector and a laminated battery having a resin current collector, particularly a sulfide solid-state laminated battery having a resin current collector.

In recent years, the use of resin current collectors for stacked batteries has been proposed (Patent Documents 1 and 2).

For example, Patent Document 2 discloses an all-solid-state lithium-ion secondary battery that includes a solid electrolyte, a positive electrode, and a negative electrode, each of which includes a resin current collector, and the resin current collector includes a base material made of a polymer material, a conductive filler, and a dispersant.

JP 2012-038426 A Japanese Patent Application Laid-Open No. 2020-087922

The present inventors have discovered that although resin current collectors have advantages such as light weight and ease of processing, depending on the application, their poor gas barrier properties compared to metal current collectors such as aluminum foil, stainless steel foil, and copper foil can be a problem.

In response to this, the present disclosure aims to solve the above problems while taking advantage of the benefits of resin current collectors, such as their light weight and ease of processing.

After extensive research, the inventors discovered that the above-mentioned problems could be solved by the following means, and thus completed the present invention. Specifically, the present invention is as follows:

<Aspect 1>
a conductive resin layer including a base resin and a conductive filler dispersed in the base resin; and a fluorine-based resin layer laminated on the conductive resin layer;
A resin current collector having the above structure.
<Aspect 2>
A stacked battery having one or more unit batteries,
a current collector on at least one end surface of the laminated battery is the resin current collector according to aspect 1; and the conductive resin layer of the resin current collector is in contact with other layers constituting the laminated battery, and the fluorine-based resin layer of the resin current collector is disposed so as to face the opposite side to the other layers constituting the laminated battery.
Stacked battery.
<Aspect 3>
3. The stacked battery according to aspect 2, wherein at least one of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer constituting the unit battery contains a sulfide solid electrolyte.

This disclosure provides a resin current collector that has improved gas barrier properties while taking advantage of the advantages of resin current collectors, such as light weight and processability, and a laminated battery that includes such a resin current collector.

FIG. 1 is a cross-sectional view showing an example of a resin current collector according to the present disclosure. FIG. 2 is a cross-sectional view showing an example of a conventional resin current collector. FIG. 3 is a cross-sectional view showing an example of a stacked battery according to the present disclosure. FIG. 4 is a graph showing the relationship between the number of cycles and the charge/discharge efficiency for the sulfide solid laminate batteries of Example 1 and Comparative Example 1. FIG. 5 is a diagram showing the evaluation results of the water vapor permeability of the resin current collectors used in Example 1 and Comparative Example 1.

Hereinafter, embodiments for implementing the present disclosure will be described in detail with reference to the drawings. However, the embodiments shown in the drawings are examples of the present disclosure and are not intended to limit the present disclosure.

<Resin current collector>
The resin current collector of the present disclosure has a conductive resin layer containing a matrix resin and a conductive filler dispersed in the matrix resin, and a fluorine-based resin layer laminated on the conductive resin layer.

In a stacked battery having one or more unit cells, the resin current collector of the present disclosure serves as the current collector on at least one end surface of the stacked battery, and the conductive resin layer of the resin current collector of the present disclosure is in contact with the other layers that make up the stacked battery, and the fluororesin layer of the resin current collector of the present disclosure is positioned facing away from the other layers that make up the stacked battery. This allows for the benefits of resin current collectors, such as light weight and processability, to be maintained while providing improved gas barrier properties due to the fluororesin layer, thereby providing the stacked battery with excellent durability.

Specifically, as shown in FIG. 1 , the resin current collector 100 of the present disclosure includes a conductive resin layer 10 containing a base resin 1 and conductive filler 2 dispersed in the base resin 1, and a fluororesin layer 20 laminated on the conductive resin layer 10. Furthermore, when using such a resin current collector of the present disclosure, as shown in FIG. 3 , in a stacked battery 1000 having one or more unit cells, the current collector on at least one end surface of the stacked battery 1000 is the resin current collector 100 of the present disclosure, the conductive resin layer 10 of the resin current collector 100 of the present disclosure is in contact with another layer 50 constituting the stacked battery 1000, and the fluororesin layer 20 of the resin current collector 100 of the present disclosure is disposed so as to face the opposite side from the other layer 50 constituting the stacked battery 1000. In such a stacked battery, the fluororesin layer of the resin current collector provides excellent gas barrier properties, thereby enabling the stacked battery to have excellent durability.

In contrast, as shown in Figure 2, a conventional resin current collector 200 does not have a fluororesin layer like the resin current collector of the present disclosure, and instead consists only of a base resin 1 and a conductive resin layer 10 containing conductive filler 2 dispersed in the base resin 1. Therefore, the present inventors have discovered that such conventional resin current collectors lack gas barrier properties, resulting in inferior durability of stacked batteries obtained using such resin current collectors.

(Conductive resin layer)
The conductive resin layer constituting the resin current collector of the present disclosure includes a matrix resin and a conductive filler dispersed in the matrix resin. This resin current collector layer may be any conductive layer known for resin current collectors. For example, the descriptions in Patent Documents 1 and 2 can be referenced for the resin current collector layer. The conductive resin layer may also be a single layer or a laminate of two or more conductive resin sublayers.

The base resin may be any thermoplastic or thermosetting resin, such as polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyethernitrile (PEN), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin, or a mixture thereof. From the standpoint of electrical stability, the base resin is preferably polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), or polycycloolefin (PCO), and more preferably polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), or a mixture thereof.

The conductive filler can be selected from any conductive material. From the viewpoint of suppressing ion permeation within the current collector, the conductive filler is preferably a material that is not conductive to the ions used as the charge transfer medium. Specifically, the conductive filler may be, but is not limited to, carbon material, aluminum, gold, silver, copper, iron, platinum, chromium, tin, indium, antimony, titanium, nickel, etc. These conductive fillers may be used alone or in combination of two or more. Furthermore, alloy materials such as stainless steel (SUS) may also be used as the conductive filler. From the viewpoint of corrosion resistance, the conductive filler is preferably aluminum, stainless steel, carbon material, or nickel, more preferably a carbon material. These conductive fillers may also be ceramic or resin materials coated with the above-listed metals by plating or other methods.

In addition to the base resin and conductive filler, the conductive resin layer may optionally further contain a dispersant for dispersing the conductive filler in the base resin. The conductive resin layer may also optionally contain other components, such as colorants, UV absorbers, plasticizers, etc. The total amount of components other than the base resin and conductive filler added may be 0.001 parts by weight or more, 0.01 parts by weight or more, 0.1 parts by weight or more, 1 part by weight or more, or 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less, per 100 parts by weight of the conductive resin layer.

(Fluorine-based resin layer)
In the resin current collector of the present disclosure, a fluororesin layer is laminated on a conductive resin layer. In the resin current collector of the present disclosure, the fluororesin has relatively high gas barrier properties, and therefore, when the resin current collector of the present disclosure is used as a current collector on the end surface of a stacked battery, it is possible to prevent ambient gas from passing through the resin current collecting layer of the present disclosure and reaching the battery stack.

The proportion of fluororesin in the fluororesin layer may be greater than 50% by mass, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more. Components other than fluororesin in the fluororesin layer may include any other resin such as those listed for the base resin of the conductive resin layer, as well as colorants, UV absorbers, plasticizers, etc. Components other than fluororesin in the fluororesin layer may include conductive fillers such as those listed for the conductive filler in the conductive resin layer, and insulating fillers such as oxides, nitrides, carbides, carbonates, or sulfates.

The fluororesin may be any resin that contains a fluorine atom (F) in its structural unit (repeating unit).

Such fluorine-based resins may be, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), fluoropolyether (FPE), perfluoropolyether (PFPE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), tetrafluoroethylene-perfluorodioxole copolymer (TFE/PDD), polyvinyl fluoride (PVF), etc.

The fluororesin layer may have a lower water vapor permeation rate than the conductive resin layer, for example, when a water vapor permeation test is carried out as follows:
Test method: JIS K 7129-4 compliant (differential pressure method)
Detector: Gas chromatograph Test gas: Water vapor (humidified atmosphere)
Temperature and humidity: 40±2°C, 90±5% (relative humidity)
Differential pressure: 1 atm

《Stacked battery》
The stacked battery of the present disclosure is a stacked battery having one or more unit batteries, wherein a current collector on at least one end surface of the stacked battery is the resin current collector of the present disclosure, the conductive resin layer of the resin current collector is in contact with other layers constituting the stacked battery, and the fluororesin layer of the resin current collector is disposed on the opposite side from the other layers constituting the stacked battery.

That is, as shown in FIG. 3, for example, this stacked battery is a stacked battery 1000 having one or more unit cells, in which the current collector on at least one end surface of the stacked battery 1000 is the resin current collector 100 of the present disclosure, the conductive resin layer 10 of the resin current collector 100 of the present disclosure is in contact with the other layers 50 constituting the stacked battery 100, and the fluorine-based resin layer 20 of the resin current collector 100 of the present disclosure is disposed so as to face the opposite side from the other layers 50 constituting the stacked battery 1000. In such a stacked battery, the fluorine-based resin layer provides excellent gas barrier properties, thereby enabling it to have excellent durability. The stacked battery of the present disclosure may also be packaged with a laminate film, such as an aluminum laminate film, as an exterior packaging.

The one or more unit batteries constituting the laminated battery of the present disclosure may be any battery. Examples of such unit batteries include lithium ion batteries, sodium ion batteries, magnesium ion batteries, and calcium ion batteries. Among these, lithium ion batteries and sodium ion batteries are preferred, and lithium ion batteries are particularly preferred.

When the unit battery is a sulfide solid-state battery, that is, a solid-state battery in which at least one of the positive electrode layer, solid electrolyte layer, and negative electrode layer that make up the unit battery contains a sulfide solid electrolyte, the performance of the unit battery is relatively likely to deteriorate in a humid environment because the sulfide solid electrolyte is prone to react with moisture.

In contrast, the resin current collector of the present disclosure can provide improved gas barrier properties due to the fluororesin layer. Therefore, the resin current collector of the present disclosure can be used particularly well when combined with a sulfide solid state battery.

Therefore, in the laminated battery disclosed herein, the unit battery is preferably a sulfide solid state battery, i.e., a solid state battery in which at least one of the positive electrode layer, solid electrolyte layer, and negative electrode layer constituting the unit battery contains a sulfide solid state electrolyte. Furthermore, this unit battery may be a lithium ion sulfide solid state battery, a sodium ion sulfide solid state battery, a magnesium ion sulfide solid state battery, a calcium ion sulfide solid state battery, or the like. Among these, this unit battery is preferably a lithium ion sulfide solid state battery or a sodium ion sulfide solid state battery, and is particularly preferably a lithium ion sulfide solid state battery.

The sulfide solid laminate battery of the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because secondary batteries can be repeatedly charged and discharged and are useful, for example, as automotive batteries. Therefore, the sulfide solid laminate battery of the present disclosure is preferably a lithium-ion sulfide solid secondary battery.

In the laminated battery disclosed herein, the unit battery is formed by stacking a positive electrode layer, a solid electrolyte layer, and a negative electrode layer in this order. The positive electrode layer may have a positive electrode current collector layer and a positive electrode active material layer, and the negative electrode layer may have a negative electrode active material layer and a negative electrode current collector layer.

The stacked battery of the present disclosure may be a monopolar battery stack or a bipolar battery stack.

(Monopolar battery stack)
When the battery stack is a monopolar battery stack, two unit batteries adjacent in the stacking direction may have a monopolar configuration in which they share a positive electrode current collector layer or a negative electrode current collector layer.

Therefore, for example, a battery stack may be a stack of two unit batteries that share a negative electrode current collector layer, and specifically may have a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, a negative electrode current collector layer, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector layer, in this order.

(Bipolar battery stack)
When the battery stack is a bipolar battery stack, two unit batteries adjacent in the stacking direction may have a bipolar configuration in which they share a positive electrode/negative electrode current collector layer that is used as both the positive electrode and negative electrode current collector layers.

Therefore, for example, a battery stack may be a stack of three unit batteries that share a positive electrode/negative electrode current collector layer used as both a positive electrode and a negative electrode current collector layer. Specifically, the battery stack may have, in this order, a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, a positive electrode/negative electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, a positive electrode/negative electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer. In this case, the "positive electrode/negative electrode current collector layer" is used as both a positive electrode and a negative electrode current collector layer, and therefore corresponds to either a "positive electrode current collector layer" or a "negative electrode current collector layer" as used in this disclosure.

(Restraint of stacked batteries)
The stacked battery of the present disclosure may be constrained in the stacking direction during use, which improves ionic and electronic conductivity within and between the layers of the battery stack during charging and discharging, thereby further accelerating the battery reaction.

In this case, the binding force is not particularly limited and may be, for example, 1.0 MPa or more, 1.5 MPa or more, 2.0 MPa or more, or 2.5 MPa or more. The upper limit of the binding force is not particularly limited and may be, for example, 50 MPa or less, 30 MPa or less, 10 MPa or less, or 5 MPa or less.

Example 1
(Preparation of Positive Electrode Active Material Layer)
A polyvinylidene fluoride (PVDF) binder (manufactured by Kureha Corporation), a positive electrode active material, a sulfide solid electrolyte ( _Li2S - _{P2S5 -} based glass ceramics), a conductive additive (vapor-grown carbon fiber (VGCF), manufactured by Showa Denko), and a solvent were added to a polypropylene (PP) container, and the resulting mixture was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT). Next, the resulting mixture was shaken in a shaker (TTM-1 manufactured by Shibata Scientific Co., Ltd.) for 3 minutes, and further stirred for 30 seconds with the ultrasonic disperser to obtain a coating solution.

The resulting coating liquid was applied to a stainless steel (SUS) foil using an applicator by the blade method, and after air drying, it was dried on a hot plate at 100°C for 30 minutes to obtain a positive electrode active material layer transfer material having a positive electrode active material layer on one surface of the stainless steel foil.

(Preparation of negative electrode active material layer)
A polyvinylidene fluoride binder (manufactured by Kureha Corporation), a negative electrode active material (lithium titanate (LTO)), the above sulfide solid electrolyte, and a solvent were added to a propylene container, and the resulting mixture was stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT) to obtain a coating solution.

The resulting coating liquid was applied to a stainless steel foil using an applicator by the blade method, and after air drying, it was dried on a hot plate at 100°C for 30 minutes to obtain a negative electrode active material layer on one surface of the stainless steel foil.

(Preparation of solid electrolyte layer)
Butyl butyrate and the sulfide solid electrolyte were added to a propylene container and stirred for 30 seconds with an ultrasonic disperser (UH-50 manufactured by SMT Co., Ltd.). Next, the resulting mixture was shaken in a shaker (TTM-1 manufactured by Shibata Scientific Co., Ltd.) for 30 minutes, and further stirred for 30 seconds with the ultrasonic disperser to obtain a coating solution.

The resulting coating liquid was applied to a stainless steel foil using an applicator by the blade method, and after air drying, it was dried on a hot plate at 100°C for 30 minutes to obtain a solid electrolyte layer transfer material having a solid electrolyte layer on one surface of the stainless steel foil.

(Preparation of resin current collector)
A fluororesin coating was applied onto the conductive resin layer using a doctor blade with a coating gap of 50 μm to obtain a resin current collector having a fluororesin layer/conductive resin layer.

(Preparation of a sulfide solid-state laminate battery for evaluation)
The solid electrolyte layer transfer material was placed on the negative electrode active material layer on the surface of the stainless steel foil, pressed, and then the stainless steel foil of the solid electrolyte layer transfer material was peeled off. This resulted in a solid electrolyte layer/negative electrode active material layer/stainless steel foil laminate. The resulting laminate was punched out to a size larger than the positive electrode active material layer obtained above.

Next, the transfer material for the positive electrode active material layer was placed on the solid electrolyte layer of the solid electrolyte layer/negative electrode active material layer/stainless steel foil laminate obtained above, pressed, and the stainless steel foil on both sides was peeled off. This resulted in a laminate having a structure of positive electrode active material layer/solid electrolyte layer/negative electrode active material layer.

Next, conductive resin layers were bonded to both sides of the resulting laminate of positive electrode active material layer/solid electrolyte layer/negative electrode active material layer to obtain the sulfide solid laminate battery of Example 1, which had a structure of resin current collector/positive electrode active material layer/solid electrolyte layer/negative electrode active material layer/resin current collector. Here, the resin current collector was positioned so that the conductive resin layer of the resin current collector was in contact with the positive electrode active material layer and the negative electrode active material layer, and the fluorine-based resin layer of the resin current collector faced away from the positive electrode active material layer and the negative electrode active material layer. Therefore, the sulfide solid laminate battery of Example 1 had a laminate structure of fluorine-based resin layer/conductive resin layer/positive electrode active material layer/solid electrolyte layer/negative electrode active material layer/conductive resin layer/fluorine-based resin layer.

The obtained sulfide solid laminate battery of Example 1 was used as the evaluation battery of Example 1. Note that all operations up to this point were carried out in a dry room environment.

Comparative Example 1
An evaluation battery of Comparative Example 1 was obtained in the same manner as in Example 1, except that a single conductive resin layer without a fluorine-based resin layer was used as the resin current collector.

"evaluation"
(Cycle characteristics of stacked battery)
Cycle evaluation was performed in the atmosphere on the evaluation batteries of Example 1 and Comparative Example 1. The measurement was performed by charging and discharging at a constant current and constant voltage within the range of 1.5 to 3.0 V at 25° C. and 0.33 C.

Figure 4 shows the change in charge-discharge efficiency with increasing cycle number, with the charge-discharge efficiency at the first cycle being 100%. As is clear from Figure 4, the sulfide solid state laminate battery of Example 1, which had a fluororesin layer on each conductive resin layer on both sides, had superior cycle characteristics compared to the sulfide solid state laminate battery of Comparative Example 1, which did not have a fluororesin layer.

(Evaluation of gas barrier properties)
The gas barrier properties were evaluated for the resin current collector used in Example 1, i.e., a resin current collector having a laminated structure of a fluorine-based resin layer/a conductive resin layer, and the resin current collector used in Comparative Example 1, i.e., a single conductive resin layer.

Specifically, a water vapor permeation test was carried out as follows to evaluate the gas barrier properties:
Test method: JIS K 7129-4 compliant (differential pressure method)
Detector: Gas chromatograph Test gas: Water vapor (humidified atmosphere)
Temperature and humidity: 40±2°C, 90±5% (relative humidity)
Differential pressure: 1 atm

The evaluation results are shown in Fig. 5, with the water vapor permeation amount of the resin current collector consisting only of a conductive resin layer (Comparative Example 1) set as the reference (1.0). As is clear from Fig. 5, the resin current collector consisting of a fluorine-based resin layer and a conductive resin layer (Example 1) had excellent protection against water vapor permeation, i.e., gas barrier properties, compared to the resin current collector consisting only of a conductive resin layer (Comparative Example 1).

1 Base resin 2 Conductive filler 10 Conductive resin layer 20 Fluorine-based resin layer 50 Portion of laminated battery other than resin current collector of the present disclosure 100 Resin current collector of the present disclosure.
200 Conventional resin current collector.
1000 Stacked battery of the present disclosure

Claims (5)

a conductive resin layer including a base resin and a conductive filler dispersed in the base resin; and a fluorine-based resin layer laminated on the conductive resin layer;
and
The fluororesin layer does not contain a conductive filler as a component other than the fluororesin.
Resin current collector (excluding those also used as packaging material for film batteries). a conductive resin layer including a base resin and a conductive filler dispersed in the base resin; and a fluorine-based resin layer laminated on the conductive resin layer;
and
The proportion of the fluorine-based resin in the fluorine-based resin layer is 99% by mass or more.
Resin current collector (excluding those also used as packaging material for film batteries). 1. A packaged stacked battery comprising: a stacked battery having one or more unit batteries; and a laminate film as an exterior packaging for packaging the stacked battery,
a current collector on at least one end surface of the laminated battery is the resin current collector according to claim 1 or 2 , and the conductive resin layer of the resin current collector is in contact with other layers constituting the laminated battery, and the fluorine-based resin layer of the resin current collector is disposed facing away from the other layers constituting the laminated battery.
Stacked battery with exterior. 4. The packaged stacked battery according to claim 3 , wherein at least one of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer constituting the unit battery contains a sulfide solid electrolyte. 4. The packaged laminated battery according to claim 3 , wherein the laminate film is an aluminum laminate film.